The distribution of the activity of brain hexokinase between soluble and mitoochondrial forms is a lease partially governed by metabolic activity, increased amounts of the particulate enzyme being observed during times of increased glycolytic activity. These changes may be involved in regulatin of activity and are thought to result from alteration in intracellular levels of various metabolites (e.g., glucose-6-P, Pi) previously shown to influence this distribution in vitro. The importance of the primary structure and conformation of the enzyme, and the role of divalent cations and various membrane constituents (e.g., lipids, proteins, glycoproteins) in this membrane-enzyme interaction will be investigated. There is also evidence to suggest that the soluble-particulate distribution may vary with cell-type. Therefore, the hexokinase levels and intracellular distribution will be determined in isolatedcell fractions from brain. In an effort to relate these observations to other metabolic properties, the fractions will also be assayed for represenative enzymes of other metabolic pathways. As an extension of the above studies, it is proposed to examine the relationship between intracellular environment and mitochondrial properties (including hexokinase content). Two systems will be employed. Using the chick optic system, we will determine the effect of axonal transport of mitochondria from the perikaryon (the site of biogenesis) to the nerve ending, cellular compartments representing considerably different biochemical environments. Using cultured neuroblastoma cells, the effect of cellular differentiation (as reflected by neurite development) on the morpoholical andenzymatic enzymatic propertis of mitochondria will be observed. The overall objective of the proposed research is to determine the factors involved in regulating the distribution of hexokinase between soluble and mitochondrial forms, and to gain an understanding of the significance of this distribution in cellular metabolism.